New (TH)GEM coating materials characterised using spectroscopy methods

TL;DR

This study investigates how different coating materials in GEM detectors influence discharge formation and stability, using spectroscopy and discharge probability measurements to identify material effects.

Contribution

It provides new insights into the material dependence of discharge phenomena in GEMs, highlighting molybdenum as a coating that enhances stability.

Findings

Light spectra include emission lines from conductive layers

No coating material lines observed during spark discharges

Molybdenum coating improves secondary discharge stability

Abstract

In this work GEM and single-hole Thick GEM structures, composed of different coating materials, are studied. The used foils incorporate conductive layers made of copper, aluminium, molybdenum, stainless steel, tungsten and tantalum. The main focus of the study is the determination of the material dependence of the formation of electrical discharges in GEM-based detectors. For this task, discharge probability measurements are conducted with several Thick GEM samples using a basic electronics readout chain. In addition to that, optical spectroscopy methods are employed to study the light emitted during discharges from the different foils. It is observed that the light spectra of GEMs include emission lines from the conductive layer material. This indicates the presence of the foil material in the discharge plasma after the initial spark. However, no lines associated with the coating material are observed while studying spark discharges induced in Thick GEMs. It is concluded that the conductive layer material does not play a substantial role in terms of stability against primary discharges. However, a strong material dependence is observed in the case of secondary discharge formation, pointing to molybdenum coating as the one providing increased stability.